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invalid value user input ask again to place into array

Scanner scanner = new Scanner(System.in);
int grade[] = new int[3];
for (int i = 0; i < grade.length; i++) {
System.out.println("Enter your test score:");
grade[i] = scanner.nextInt();
}
I've been trying to figure out how to make it so if the user input is below 0 or above 100 it will ask again. I'm very new to Java and this is the first language I'm learning. I would appreciate any pointers. Do I need to use a do-while loop instead of a for loop for this? Or do I implement an if statement into the for loop?

You can validate the input by putting an if block inside the for loop.
However, since your loop will only execute three times, you should change your increment condition only when user enters correct input or else not.
You also can use while loop here.
Here is some example code:
for (int i = 0; i < grade.length; i++)
{
System.out.println("Enter your test score:");
if(grade[i] < 0 || grade > 100)
{
i--;
continue;
}
grade[i] = scanner.nextInt();
}
The if block will check that if the input is outside boundaries, decrement i and restart the loop.

What I suggest is, instead of incrementing i in loop, you can increase the value in if condition. Like below,
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int grade[] = new int[3];
for (int i = 0; i < grade.length;) {
System.out.println("Enter your test score:");
int temp = scanner.nextInt();
if (temp >= 0 && temp <= 100) {
grade[i] = temp;
i++;
}else {
System.out.println("Please enter valid score");
}
}
scanner.close();
}
This basically gets a input value from user, if the value is greater or equal to 0 && lesser or equal to 100,then adds it to the Array and increments the loop count(array index value we can call it), else, prints message asking for valid input.

Instead of shoving the validation logic somewhere within the loop, you could also write a small utility method which neatly asks for valid input, and continues to do so until the user finally inputs something valid:
int promptInt(Scanner scanner, int min, int max, String errorMessage) {
while (true) {
int input = scanner.nextInt();
if (min <= input && input <= max) {
return input;
}
else {
System.out.println(errorMessage);
}
}
}
You could then simplify the loop:
int grade[] = new int[3];
for (int i = 0; i < grade.length; i++) {
System.out.println("Enter your test score:");
grade[i] = promptInt(0, 100, "Please enter a valid number");
}

User input never enters if statement

The point of the program is to have a user input an amount of integers endlessly (until they enter something other than an integer), and for each integer the user inputs, it should check if the integer is greater than or less than the value entered.
The problem: When the program runs, everything is fine until reaching
number = scanner.nextInt();
At this point, the user inputs their integer, but never makes it inside the following if statements. I would love a hint instead of an answer, but I'll take what I can get.
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
do {
System.out.println("Enter number: ");
int number = 0;
int minNumber = 0;
int maxNumber = 0;
boolean hasInt = scanner.hasNextInt();
if (hasInt) {
number = scanner.nextInt();
if (maxNumber < number) {
maxNumber = number;
}
if (minNumber > number) {
minNumber = number;
}
} else {
System.out.println("Your minimum number: " + number);
System.out.println("Your maximum number: " + maxNumber);
break;
}
} while (true);
scanner.close();
}
}

Your minNumber and maxNumber declarations should be out side of the loop. Also, you need to initialize the values as below to get correct min and max comparison with the entered values only:
int minNumber = Integer.MAX_VALUE;
int maxNumber = Integer.MIN_VALUE;
In print statement instead of minNumber you are printing number!

It's not reaching the if statements, because if it did, the user input would update to the value entered I would think. It doesn't. It outputs the values initially declared.
You're not getting the right output and you have a hypothesis that the cause is the code not entering the if statements. Following the scientific method, the next step is to test your hypothesis.
If you put printouts inside the if statements you'll see that they are indeed running. That's not it. The mistake must be elsewhere. You should collect more evidence and develop a new hypothesis.
Hint: Try printing out the values of your variables at the beginning and end of each iteration. I've marked the places below. Are they what you expect them to be? You're going to see an anomaly that should point you in the right direction.
do {
System.out.println("Enter number: ");
int number = 0;
int minNumber = 0;
int maxNumber = 0;
// Print number, minNumber, and maxNumber.
boolean hasInt = scanner.hasNextInt();
if (hasInt) {
number = scanner.nextInt();
if (maxNumber < number) {
maxNumber = number;
}
if (minNumber > number) {
minNumber = number;
}
} else {
System.out.println("Your minimum number: " + number);
System.out.println("Your maximum number: " + maxNumber);
break;
}
// Print number, minNumber, and maxNumber.
} while (true);

For loop to get user input lets you enter two values for the first question, but only calculates one value

I created a small program that asks the user for 10 random numbers and it will print the sum of those numbers. I embedded it with a for loop and included a counter. Everything seems to be working fine except when I run the program, the first question allows me to enter two values, but it will still only calculate a total of 10 numbers.
Below is what I currently have and I need to understand what is going wrong when it prompts the user for the number the first time:
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
int sum = 0;
int counter = 0;
for (int i = 0; i < 10; i++) {
counter++;
System.out.println("Enter number #" + counter + " :");
int numberInput = scanner.nextInt();
boolean hasNextInt = scanner.hasNextInt();
if (hasNextInt) {
sum += numberInput;
} else {
System.out.println("Invalid Number");
}
}
scanner.nextLine(); // handle the next line character (enter key)
System.out.println("The sum is " + sum);
scanner.close();
}
}

In each loop, you're calling scanner.nextInt() and scanner.hasNextInt(). But you do not use the result of hasNextInt() in a meaningful way (you might have noticed that your "Invalid Number" output is not what happens if you enter something that's not a number).
The first call to nextInt() blocks until you enter a number. Then hasNextInt() will block again because the number has already been read, and you're asking whether there will be a new one. This next number is read from System.in, but you're not actually using it in this iteration (you merely asked whether it's there). Then in the next iterations, nextInt() will not block because the scanner already pulled a number from System.in and can return it immediately, so all the subsequent prompts you see actually wait for input on hasNextInt().
This amounts to 11 total input events: The firts nextInt() plus all 10 hasNextInt()s

Scanner scanner = new Scanner(System.in);
int sum = 0;
int counter = 0;
for (int i = 0; i < 10; i++) {
counter++;
System.out.println("Enter number #" + counter + " :");
int numberInput = scanner.nextInt();
// boolean hasNextInt = scanner.hasNextInt();
//if (hasNextInt) {
sum += numberInput;
// } else {
// System.out.println("Invalid Number");
//}
}
scanner.nextLine(); // handle the next line character (enter key)
System.out.println("The sum is " + sum);
scanner.close();
Don't call hasnextInt() it has no use here.
It has taken 11 inputs rather than 10.
If you remove this condition it will take 10 inputs and work fine.
Your condition have no impact on it.

Java - No Duplicate number array

I am in the process of creating of a Lottery Program using Java via BlueJ and I am having trouble with the user inputted numbers and the number being generated by the program (up to and including 1-49), I need the numbers that are entered by the user to not be duplicate i.e. the user cannot enter 1 and 1.
I am not really sure how to get the numbers to not be duplicate i was thinking of using an Array but im not sure what type or where to begin im rather new to the whole programming thing.
import java.util.Arrays;
import java.util.Random;
import java.util.Scanner;
public class JavaApplication8 {
public static void main(String[] args) {
Scanner user_input = new Scanner (System.in);
Scanner keyIn = new Scanner(System.in);
int[] LotteryNumbers = new int[6];
int input;
int count = 0;
System.out.print("Welcome to my lottery program which takes\nyour lottery numbers and compares\nthem to this weeks lottery numbers!");
System.out.print("\n\nPress the enter key to continue");
keyIn.nextLine();
for (int i = 0; i < LotteryNumbers.length; i++)
{
count ++;
System.out.println("Enter your five Lottery Numbers now " + count + " (must be between 1 and 49): ");
input = Integer.parseInt(user_input.next());
if (input < 1 || input > 49)
{
while (input < 1 || input > 49)
{
System.out.println("Invalid number entered! \nPlease enter lottery number (between 1 and 49) " + count);
input = Integer.parseInt(user_input.next());
if (input >= 1 || input <= 49)
{
LotteryNumbers[i] = input;
}
}
}
else
{
LotteryNumbers[i] = input;
}
}
System.out.println("Thank you for your numbers.\nThe system will now check if you have any matching numbers");
System.out.print("Press the enter key to continue");
keyIn.nextLine();
Random randNumGenerator = new Random();
StringBuilder output = new StringBuilder();
int[] ActLotteryNumbers = new int[6];
for (int j = 0; j < ActLotteryNumbers.length; j++)
{
int roll = randNumGenerator.nextInt(49);
ActLotteryNumbers[j] = roll;
}
System.out.println(Arrays.toString(ActLotteryNumbers));
int counter = 0;
for (int i = 0; i < LotteryNumbers.length; i++)
{
for (int j = 0; j < ActLotteryNumbers.length; j++)
{
if (LotteryNumbers[i] == ActLotteryNumbers [j])
{
counter ++;
System.out.println("The numbers that match up are: \n" + LotteryNumbers[i]);
}
}
}
if (counter == 0)
{
System.out.println("You had no matching numbers this week ... Try Again next week!");
}
}
}

As "fge" mentioned, use Set to add all the values that you are getting from the user.
Get the user inputs and add it to Set.
Use a Iterator to check the user entered values and generated random numbers.
Set myset = new HashSet();
myset.add(user_input1);
myset.add(user_input1);
To retrive use the iterator'
Iterator iterator = myset.iterator();
while(iterator.hasNext(){
int value= iterator.next();
if(randomValue==value)
//do your logic here
}

I am assuming this is for a school project/lab? (This is due to the JavaApplication8 class name) If that is the case, what the instructor is most likely looking for is a contains method.
For a contains method you write a method that takes an integer and checks to see if it is already in your LotteryNumbers array and returns a boolean. It would return true if it is in the array, false if it is not in it. This method would be called before inserting the number into LotteryNumbers. You could use your count variable that doesn't appear to be used anywhere else as the limit on your loop in the contains method to avoid checking uninitialized entries.
If there is no restriction on type, the set idea suggested by others works and is more efficient, it just depends on what you are supposed to be using for your requirements.
Additionally, the logic you use should most likely be applied to ActLotteryNumbers as well. If you can't have duplicates incoming, you shouldn't have duplicate values in the comparing array. Lottery isn't fair in real life, but not that unfair ;-)
First step should be checking your restrictions on this project.

Terminating loops with strings. (Java)

Write a program that uses a while loop. In each iteration of the loop, prompt the user to enter a number – positive, negative, or zero. Keep a running total of the numbers the user enters and also keep a count of the number of entries the user makes. The program should stop whenever the user enters “q” to quit. When the user has finished, print the grand total and the number of entries the user typed.
I can get this program to work when I enter a number like 0, to terminate the loop. But I have no idea how to get it so that a string stops it.
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int count = 0;
int sum = 0;
int num;
System.out.println("Enter an integer, enter q to quit.");
num = in.nextInt();
while (num != 0) {
if (num > 0){
sum += num;
}
if (num < 0){
sum += num;
}
count++;
System.out.println("Enter an integer, enter q to quit.");
num = in.nextInt();
}
System.out.println("You entered " + count + " terms, and the sum is " + sum + ".");
}

Your strategy would be to get the input as a string, check to see if it is a "q", and if not convert to number and loop.
(Since this is your project, I am only offering strategy rather than code)
This is the rough strategy:
String line;
line = [use your input method to get a line]
while (!line.trim().equalsIgnoreCase("q")) {
int value = Integer.parseInt(line);
[do your work]
line = [use your input method to get a line]
}

public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int count = 0;
int sum = 0;
String num;
System.out.println("Enter an integer, enter q to quit.");
num = in.next();
while (!num.equals("q")) {
sum += Integer.parseInt(num);
count++;
System.out.println("Enter an integer, enter q to quit.");
num = in.next();
}
System.out.println("You entered " + count + " terms, and the sum is " + sum + ".");
}
Cuts down on your code abit and is simple to understand and gives you exactly what you want.
could also add an if statement to check if they entered another random values(so program doesn't crash if the user didn't listen). Something like:
if(isLetter(num.charAt(0))
System.out.println("Not an int, try again");
Would put it right after the while loop, therefore it would already of checked if it was q.

java expects an integer but we should give the same exception. One way to solve this problem is entering a String, so that if the user first pressing is the Q, never enters the cycle, if not the Q. We assume that the user is an expert and will only enter numbers and the Q when you are finished. Within the while we convert the String to number with num.parseInt (String)
Integer num;
String input;
while(!input.equal(q)){
num=num.parseInt(input)
if(num<0)
sum+=1;
else
sumA+=1;
}